This invention relates to columbium powders and to anodes prepared therefrom, and specifically to powders capable of producing anodes improved in electrical capacitance.
The use of columbium powders for the preparation of electrodes in electrolytic capacitors is well-known. Columbium powders are known to be suitable as a lower cost substitute for tantalum powders in electrolytic capacitors, particularly in low voltage applications. Columbium electrodes are made by pressing a columbium powder to form a coherent compact, sintering the compact and subsequently forming a dielectric film on the sintered product. In such capacitors, it is desired to have as high a specific capacity (CV/g.) as possible. Tantalum powder, as disclosed in U.S. Pat. No. 3,418,106, is improved with respect to specific capacity when it is first agglomerated, then crushed as tantalum, and finally fabricated into an electrode.
U.S. Pat. No. 3,825,802 discloses improvements in various properties of tantalum capacitors, including specific capacity, by the addition to the tantalum of any of several "dopants", including phosphorus. The range of "dopant" disclosed is from 0.47 to 2.71 atomic percent which, for phosphorus is equivalent to from about 800 to 4600 parts per million and the improvement in specific capacity (with nitrogen, the preferred species) ranges from about 2% (at the lower end of the range) to about 6.3% (at the upper end) when the anode is sintered at 1900.degree. C.
My copending and co-assigned U.S. Pat. No. Application Ser. No. 595,569 filed July 14, 1975, now U.S. Pat. No. 4,009,007 discloses that substantial improvement in the specific capacity of tantalum powder may be obtained by the addition thereto of phosphorus-containing materials in amounts from about 5 to about 400 ppm based on elemental phosphorus.